A coordinate measuring machine configured to move a probe in three dimensions with respect to a workpiece (measurement target) has been known as a profile measuring machine. A portal movement mechanism straddling the workpiece is used in a large-sized coordinate measuring machine (see Patent Literature 1: JP2010-122118A).
The portal coordinate measuring machine includes: a table on which the workpiece is placed; a pair of columns provided on both sides of the table; a beam bridging the pair of columns and extending in an X-axis direction; a slider capable of moving on and along the beam; a Z-spindle configured to be moved up and down relative to the slider; and a probe attached to a lower end of the Z-spindle. The columns and the beam are moved in a Y-axis direction relative to the table, the slider is moved along the beam in the X-axis direction, and the Z-spindle is moved in a Z-axis direction (up-down direction) relative to the slider, whereby the probe can be moved in three dimensions on the table relative to the workpiece. The respective movements in the X-axis, Y-axis and Z-axis directions are conducted by X-axis, Y-axis and Z-axis movement mechanism each in a form of a motor and the like.
In a typical movement mechanism configured to relatively move the table and the column in the Y-axis direction, for instance, a lateral surface of the table is defined as a guide surface and a roller is rolled on the guide surface (see Patent Literature 2: JP2016-142542A).
Specifically, highly flat guide surfaces are formed on both sides of an upper surface and lateral surfaces of the table. Air pads (static-pressure air bearings) are provided to the pair of columns in a manner to face the corresponding guide surfaces. Among the air pads, the air pads facing the upper surface of the table support loads of the corresponding columns. The columns are guided in the Y-axis direction by the air pads sandwiching both the lateral surfaces of the table.
A drive roller configured to roll on the lateral surface of the table is provided to one of the columns. Since the drive roller drives the one of the columns to move relative to the table, the entire portal structure, including the beam and the other column, are moved in the Y-axis direction relative to the table.
A friction-force-reinforcement material (e.g., urethane, rubber, and a silicon resin) having a thickness in the order of several mm is attached to a surface of the roller in order to reinforce a friction force applied on the table.
As described above, the region on which the drive roller rolls and the guide surface that the air pads face are provided to one of the lateral surfaces of the table.
In a typical arrangement as described in Patent Literature 2 and the like, the region of the drive roller and the guide surface overlap each other. Specifically, a pair of guiding air pads are provided to the column that is to be driven to move, and the drive roller is interposed between the pair of air pads and is configured to roll on the guide surface.
In this arrangement, the rolling of the roller sometimes causes the friction-force-reinforcement material on the roller surface to be worn into fine particles, resulting in adhesion of the fine particles to the guide surface.
The adhesion of the fine particles and the like to the guide surface impairs flatness and smoothness of the guide surface, which may hamper an appropriate static pressure floating of the air pads with a small interval, resulting in a loss of a desired guide function. However, if a hardness and a strength of the friction-force-reinforcement material are increased to avoid generation of the fine particles, the drive performance of the drive roller may fall below an appropriate level.